Method for forming lined container closures



p 1952 D. L. SHANKLIN ET,AL 2,610,131

METHOD FOR FORMING LINED CONTAINER CLOSURES Original' Filed Feb. 21,1949 'IHHI'III 1 WwrmmiW W- 2- 1 DU/VBAR L. SHA/VKL/N R/CHARD C. ADAMSPatented Sept. 9, 1952 METHOD FOR FORMING LINED CONTAINER CLOSURESDunbar L. Shanklin, Winchester, and Richard C. Adams, Cambridge, Mass,assignors to Dewey and Almy Chemical Company,

Cambridge,

Mass., a corporation of Massachusetts Original application February 21,1949, Serial No. 77,622. Divided and this application April 27, 1950,Serial No. 158,486

This application is a division of our copending application Serial No.77,622, filed February 21, 1949.

This invention is concerned with a process of forming lined containerclosures, especially of the type for sealing glass containers where thesealing surface of the container may be irregular. The invention dealsespecially with the formation of sealing gaskets on container closuresfrom sealing material formed of paste resin-plasticizer mixtures whichmust be baked after being applied to the closures in order to causefluxing of the gasket material.

In the closure art, gaskets of sealing material which form the hermeticjoint between the container parts are known as linings and the operationof applying the gasket to the closure is known as closure lining orsimply lining. Hereafter, in order to adopt a phraseology which isconsistent with the art, the word lining will be used.

Where the lining is being formed on a closure having a decorative designon the outer surface and a protective coating on the inner surface, thefiuxing step introduces a problem in preventing damage to the decorativeand protective coatings from the heat required to flux the lining.

The invention is also concerned with a baking oven especially designedfor carrying out the process of the invention.

The manufacture of glass, although much improved in accuracy, stillproduces jars which are grossly inaccurate when compared to themechanical standardsexisting in metal fabrication. The rim of a glassjar lies only in an approximate, not a true, plane, and the eccentricityof its diameter varies very frequently as much as a 32nd of an inch. Asa result, closures for glass jars are called upon to seal wide gaps.This requirement, in turn, demands that the sealing element of a glassclosureshould be thick enough and deformable enough to compensate forall of the irregularities in the glass finish.

The necessity for applying a large quantity of sealing material to theclosure in forming the lining has always caused difficulties in thepast. The application has been slow ascontrasted with can manufacture,and the drying and cure of the sealing material has been both slow anddifilcult.

The technology ofplacing thick linings on closures for glass containershas been greatly aided by the development of the so-ca-lled pastesealing compounds. Paste's are liquid or plastic systems-comprised ofsmall particles 6 Claims. (01. 117-65) of a synthetic resin, which aresuspended in a liquid plasticizer. Paste-forming resins must have thepeculiar property of being substantially insoluble in the plasticizer atthe atmospheric temperatures which are normally encountered, but theymust be completely soluble in the plasticizer at some considerablyhigher temperature. When pastes are heated, and after the resin has goneinto solution, a gel is formed which turns into a permanent, rubbery andelastic substance after it has cooled.

Since paste technology eliminates the necessity for driving off theliquid carrier which previously had to be used in all sealing compoundswhich were applied to the closu're in liquid form, for example, thewaterof latex, the manufacture of glass closures has'become a very rapidprocedure. But the use of pastes has, in turn, introduced anotherserious problem because it is necessary to heat the paste-lined closureto a high temperature in order to convert the paste into the rubberygel. The temperature of pastegel conversion is of the same orderofmagnitude as are the temperatures which destroy the lithographic designson the outer surface and the protective coating'on the interior of theclosure.

When paste compounds are fluxed on coated container closures, thecoating frequently becomes brittle and usually changes color. Often, thewhite coating on the interior of a closure changes to spotty, dirty grayor to tan and even to coffee brown shades after the lining has beenapplied and lluxed. This change in, color, it nothing more, makes theclosures unsalahle, for the public associates brightness and whitenessof the coating with the retention of quality in the foodstuff. Althoughthere is no reason why a housewife should throw away a jar of mayonnaiseor of peanut butter if the coating of the closure is colored or stained,nonetheless she does. The grocer then has a complaint and returned goodson his hands. The maintenance of unchanged appearance of the coating,therefore, has a high degree of economic significance.

In studying the darkening of the commercial tin-plate coatings at the.degree of heat necessary to flux paste-lining compositions, wediscovered that there is an induction period before any noticeablechange occurs. For example, a white closure-coating may be exposed to ahigh temperature for a certain minimum period and no change will benoted. After the time threshold has expired, darkening progresses withgreat rapidity. 'We found that the thresholds vary from coating tocoating and that the products of different manufacturers; havematerially the medium which imparts heat to the object.

Since we had determined that the threshold,

before darkening of the coating, was a timetemperature relationship, wefound that in ovens of conventional design using still air, or airmoving at low velocity, as the heat transfer medium, the temperature ofthe heat transferring medium had to be raised so high that, if theclosures were to be heated, fluxed and cooled before the darkeningcommenced, the time value became vanishingly small, so small in factthat it was not possible to handle the closures in the time available.

This invention permits the fluxing operation, i. e., the heating stepwhich converts the paste to the gel, to be conducted at the requisitetemperature but prevents damage to the lithography or protective coatingfrom occurring. The invention also produces container closure-liningswhich have materially enhanced elastic properties as contrasted tolinings of conventionally heated pastes with the result that theyconform more readily to the inaccuracies of the glass finish.

According to our invention, we achieve rapid heating, by first heating alarge volume of air to a temperature not in excess of 5 F. above thetemperature chosen for the fluxing operation and then propel this largevolume of heated air against the lined closure at such a velocity thatthe temperature of the closure rises to the fluxing temperature within aperiod of sixty seconds and preferably even more quickly. We can achievethis rapid rate of heating if the minimum average velocity of the heatedair is maintained at or'above 1500 feet per minute. We then remove theclosures from the heating zone so quickly and cool them s that the totalexposure to heat will never exceed two minutes.

By heating a large volume of air, then forcing 7 it at high velocityagainst the closure, we transfer a sufficient number of heat units tothe sealing element in a short enough time to accomplish our purpose,although the temperature of the air mass is substantially that of thefiuxing temperature of the compound. Closures, when treated in thismanner, maintain unchanged the original characteristics of thelithography and protective coating.

The surprising discovery was then made that the gels which were formedby bringing the mass to its maximum temperature in a few seconds showeda higher penetration (greater softness) for a given percentageelongation than did gels which were subjected to the same maximumtemperature, but reached that temperature more slowly.

At present, we cannot explain this phenomenon. Whatever its reason maybe, we have found, by averaging the results of many determinations ofsoftness as measured by the Ames penetrometer, that linings produced byour quickgram heating process are 30% softer than linings fiuxed to thesame percentage elongation but heated in a conventional oven; Forexample, to produce a lining having 250% elongation at break required aprocessing time of only 45 seconds in our quick-heating process andproduced a penetration of 28, whereas producing a lining having the samepercentage elongation by heating in a standard electric 'oven required 3minutes and resulted in a penetration of only 21.

Of course, it ispossible to increase the softness of any plasticizedcompound by increasing the ratio f plasticizer to resin, but this is nota proper solution of the softness problem in a container sealingcompound. The reason is that such compounds .are thermoplastic and thegreater the ratio of plasticizer to resin, the more thermoplastic thecompound becomes. Since most foods are packed hot, the danger of cuttingthrough the seal when the cap is turned down or when the cap is urgedtowards the glass by the differential pressure between atmospheric andthe reduced internal pressure increases as the proportion of plasticizerincreases. 1 Hence, any expedient which increases softness without atthe same time increasing the proportion of plasticizer in the compoundis of great valuein container sealing technology.

Both phases of our invention will be described below with reference tothe accompanying drawing in which: V

Figure 1 is a diagrammatic showing of apparatus suitable forperformingthe process of the invention Figure 2 is a plan view of aportion of theconveyor belt showing a number of enclosures positionedthereon. 1 r

In Figure 1 of the drawing suitable apparatus for carrying out theprocess of the invention is illustrated in diagrammatic form. Thefreshly lined container closures are placed, upon a moving conveyor A ofopen meshwor-k construction which moves the closures in a horizontalplane;

through a heating zone or chamber in which heated air is blownvertically downward against the closures carried by the conveyor A. Inmost cases, the lined closures will be placed upon'the conveyor withtheir lined faces turned upwardly.

The heating medium acting on the closures and passing through theheating zone is supplied from an oven system formed of a heater 13having itsintake connected to the lower'portion C of a heating chamberthrough which the conveyor moves and having its output connected to theintake of the blower D; The outlet of the blower chamber in which air ata considerably reduced. temperature is blown transversely through the.conveyor to cool the closures as. rapidly as maybe required according tothe speed'cf movement of the conveyor. The arrangement for supplying thecooling air is represented by a blower F mounted on top of the upperportion G of the cooling chamber. The cooling air after pass- Oven usedfor comparison Precision-Freas Model 605 mechanical convection constanttemperature type.

5. ing through the conveyor enters the lower part H of the coolingchamber and is conducted out of the building through the conduit I.

Figure 2 shows a plan view of a section of the conveyor A whichconveniently may assume the form of an endless flexible belt. Anysuitable construction of belt may be used but it is important to have anopen mesh construction which has a very high percentage of open spacecompared with the closed space. For fastest heating of the closures, theclosures should be spaced apart when they are placed on the conveyor toprovide at least 50% free area for the passage of heated air through theconveyor and around the edges of the closures. In practice, it will befound that the open space through the conveyor when loaded with closuresmay vary from 30 to 70%, depending on the size and shape of theclosures.

In carrying out the process of our invention, the factors which must becontrolled are the speed of the conveyor A, the temperature of theheating medium as it impinges upon the closures in passing through theheating zone, and the velocity of the heating medium. These factors mustbe correlated to secure proper fluxing of the linings on the closures asthey pass through the heating zone without injuring or damaging thedecorative and protective coatings on the closures. From" the standpointof commercial production, it is also highly important to speed up theprocess.

Our process is especially useful in fluxing 1111- ings formed ofso-called paste sealing compound of the type referred to previously. Inpaste resins based on polyvinyl chlorides, the mass temperature of theheating medium is conveniently maintained at 350 F., the velocitythrough the conveyor is maintained above 2000 feet per minute and up toany higher value which conveniently may be obtained (this value is to alarge degree controlled by the size of the container closures) and totaltime in the oven may be from 20 to 90 seconds depending on the thicknessand type of the lining.

The movement of the heating medium at a high velocity is important inour process in obtaining quick heating with a small differential betweenthe temperature of the medium and the object to be heated. While we donot wish to be limited to any particular theory of explanation of theaction, it is believed that the sudden 90" change in direction of a highvelocity air stream as it impinges upon the exposed surface of theclosures produces a highly turbulent, scouring flow across the closurewhich greatly aids in imparting heat both to the metal and to thecompound surfaces of. the closures, because it destroys the skin ofstatic air which usually clings to a surface despite a moving aircurrent. The heat imparted to the metal is conducted to the outerperipheraledges of the closures and imparted to the lining compoundthrough the back surface. At the same time, heat is being supplied tothe lined compound by direct impingement of the air stream upon thelining material. Assuming that the area of the lining is 50% of theexposed area of the closure, then the compound receives about an equalamount of heatby its direct exposure to the air and by conductionthrough the metal to its undersurface.

While difierent forms of apparatus may be devised for carrying out ourprocess, a novelform of oven especially designed'to carry out theprocess is disclosed in our copendingapplication serial No. 77,622,filed February 21, 1949.

We claim:

1. The process of fiuxing linings on container closures while retainingthe protective or lithographic coating on the closure in an undamagedcondition by heating the closure in a blast of heated air, said liningsbeing formed of a plastisol comprising small particles of apaste-forming synthetic resin suspended in a non-volatile plasticiserfor the resin, said resin being substantially insoluble in theplasticizer at atmospheric temperatures but being completely soluble inthe plasticizer at an elevated fluxing temperature and forming at thiselevated temperature a permanent gel which becomes elastic and rubberyupon subsequent cooling which comprises arranging the lined closures onan open mesh sup" port, said support being of such open mesh that whenit is loaded with closures to be treated 30 to 70% of its area is stillfree for the passage of air therethrough, directing a continuous streamof heated air upon said closures and around and past the same, saidstream continu ously discharging through said mesh support, said airbeing heated to a temperature not sub stantially less than 300 F.sufficient to flux the lining and not greater than the temperature atwhich the coating on the closures would discolor within a heating timeof two minutes, said now of air having a velocity through the free areasof the support in excess of 1500 feet per minute and SLlfilCiEIll; tocause the closures to attain a temperature within 5 F. of thetemperatureof the heated air within a period not exceeding 60 seconds, removing thefluxed closures from the stream of heated air within a period such thatthe overall time of exposure to the heated air is less than two minutesand cooling the closures.

2. The process of fluxing linings on container closures while retainingthe protective or lithographic coating on the closure in an undamagedcondition by heating the closure in a blast of heated air, said liningsbeing formed of a plastisol comprising small particles of a pasteformingsynthetic resin suspended in a nonvolatile plasticizer for the resin,said resin being substantially insoluble in the plasticizer atatmospheric temperatures but being completely soluble in the plasticizerat an elevated fluxing temperature and forming at this elevated tern--perature a permanent gel which becomes elastic and rubbery uponsubsequent cooling which comprises arranging the lined closures on anopen mesh support, said support being of such open mesh that when it isloaded with closures to be treated 30 to 70% of its area is still freefor the passage of air therethrough, spacing the closures on the supportto provide at least 50% free area, directing a continuous stream ofheated air upon said closures and around and past the same, said streamcontinuously discharging through said mesh support, said air beingheated to a temperature not substantially less than 300 F. sufficient toflux the lining and not greater than the temperature at which thecoating on the closures would discolor within a heating time of twominutes, said flow of air having a velocity through the free areas ofthe support in excess of 1500 feet per minute and sufiicient to causethe closures to attain a temperature within 5 f. of the temperature ofthe heated air within a period not exoeedingfiO seconds, removing thefluxed closures from the stream of heated air. within a period such thatthe overall time otexposur'e to the heated air is less than two minutesand cooling the closures.

3. The process of fluxing linings on container closures while retainingthe protective or lithographic coating on the closure in an undamagedcondition by heating the closure in a blast of heated air, said liningsbeing formed of a plastisol comprising small particles of apaste-forming synthetic resin suspended in a non-volatile plasticizerfor the resin, said resin being substantially insoluble in theplasticizer at atmospheric temperatures but being completely soluble inthe plasticizer at an elevated fluxing temperature and forming at thiselevated temperature a permanent gel which becomes elastic and rubberyupon subsequent cooling which comprises arranging the lined closures onan open mesh support, said support being of such open mesh that when itis loaded with closures to be treated 30 to 70% of its area is stillfree for the passage of air therethrough, directing a continuous streamof heated air upon said closures and around and past the same, saidstream continuously discharging through said mesh support, said airbeing heated to a temperature not substantially less than 300 F.sufiicient to flux the lining and not greater than the temperature atwhich the coating on the closures would discolor within a, heating timeof two minutes, said flow of air having a velocity through the freeareas of the support in excess of 1500 feet per minute and suiiicient tocause the closures to attain a temperature within F. of the temperatureof the heated air within a period not exceeding 60 seconds, said flow ofair impinging upon the closures at substantially a right angle to theplane of the closures, removing the fluxed closures from the stream ofheated air within a period such that the overall time of exposure to theheated air is less than two minutes and cooling the closures.

4. The process of fluxing linings on container closures while retainingthe protective orlithographic coating on the closure in an undamagedcondition by heating the closure in a blast of heated air, said liningsbeing formed of a plastisol comprising small particles of apaste-forming synthetic resin suspended in a non-volatile plasticizerfor the resin, said resin being substantially insoluble in thepasticizer at atmospheric temperatures but being completely soluble inthe plasticizer at an elevated fluxing temperature and forming at thiselevated temperature a permanent gel which becomes elastic and rubberyupon subsequent cooling which comprises arranging the lined closures onan open mesh support, said support being of such open mesh that when itis loaded with closures to be treated 30 to 70% of its area is stillfree for the passage of air therethrough, directing a continuous streamof heated air upon said closures and around and past the same, saidstream continuously discharging through said mesh support, said airbeing heated to a temperature in excess of the fluxing temperature andnot substantially less than 300 F. at which the coating discolors ifexposed to said temperature for a period of two minutes, said flow ofair having velocity through the free areas of the support in excess of1500 feet per minute and sufficient to cause the closures to attain atemperature within 5 F. of the temperature of the heated air within aperiod not exceeding 60 seconds, removing the fiuxed closures from thestream of heated air within a, period such that the overall time ofexposure to the heated'air is less than two minutes and cooling theclosures.

5.' The process of fiuxing linings on container closures while retainingthe protective or lithographic coating on the closure in an undamagedcondition by heating the closure in a blast of heated air, said liningsbeing formed of a plastisol comprising small particles of apaste-forming synthetic resin suspended in a non-volatile plasticizerfor the resin, said resin being substantially insoluble in theplasticizer at atmospheric temperatures but being completely soluble inthe plasticizer at an elevated fluxing temperature and forming at thiselevated temperature a, permanent gel which becomes elastic and rubberyupon subsequent cooling which comprises arranging the lined closures onan open mesh support, said support being of such open mesh that when itis loaded with closures to be treated 30 to 70% of its area is stillfree for the passage of air therethrough, directing a continuous streamof heated air upon said closures and around and past the same, saidstream continuously discharging through said mesh support, said airbeing heated to a temperature 5 F. above a predetermined fiuxingtemperature not substantially less than 300 F., said flow of airhaving avelocity through the free areas of the support in excess of 1500 feetper minute and sufficient to cause the closures to attain a tem peraturewithin 5 F. of the temperature of the heated air within a period notexceeding 60 seconds, removing the fluxed closures from the stream ofheated air and rapidly cooling them within a period such that theoverall time of exposure of the closures of heat is less than twominutes.

6. The process of fluxing container closure linings formed of aplastisol comprising small particles of a paste-forming synthetic resinsuspended in a non-volatile plasticizer for the resin, said resin beingsubstantially insoluble in the plasticizer at atmospheric temperaturesbut being completely soluble in the plasticizer at an elevated fluxingtemperature and forming at this elevated temperature a permanent gelwhich becomes elastic and rubbery upon subsequent cooling, whileretaining the protective or lithographic coating on said closures in anundamaged condition by heating the closures in a blast of heated airwhereby the lining, as contrasted With normally fluxed linings ofidentical composition having the same percentage elongation beforebreak, exhibits materially greater softness which comprises arrangingthe lined closures on an open mesh support, said support being of suchopen mesh that when it is loaded with closures to be treated 30 to 70%of its area is still free for the passage of air therethrough, directinga continuous stream of heated air upon said closuresan'daround and pastthe same, said stream continuously discharging through said meshsupport, said air being heated to a temperature not substantially lessthan 300 F. sufficient to flux the lining and not greater than thetemperature at which the coating on the closures would discolor within aheating time of two minutes, said flow of air having a velocity throughthe free areas of the support in excess of 1500 feet per minute andsufiicient to cause the closures to attain a temperature within 55 F. ofthe temperature of the heated air Within a period not exceeding 60seconds, removing the fluxed closures from the stream of heated airwithin a period such 10 that the overall time of exposure to the heatedUNITED STATES PATENTS air is less than two minutes and cooling the clo-Number Name Date sures- 2,072,536 Trickey Mar, 2, 1937 DUNBAR L.SHANIGJIN. ,333,522 Beadle NOV. 9, 1943 RICHARD c. ADAMS. 5 2,354,855},Emanuel Aug. 1, 1944 2,426,413 Pollett Aug. 26, 1947 REFERENCES CITED 6:y N0V- 1950 The following references are of record in the OTHERREFERENCES file of this patent: 10 Baird: British Plastics, April 1948,pp. 167-171.

1. THE PROCESS OF FLUXING LININGS ON CONTAINER CLOSURES WHILE RETAININGTHE PROTECTIVE OR LITHOGRAPHIC COATING ON THE CLOSURE IN AN UNDAMAGEDCONDITION BY HEATING THE CLOSURE IN A BLAST OF HEATED AIR SAID LININGSBEING FORMED OF A PLASTISOL COMPRISING SMALL PARTICLES OF APASTE-FORMING SYNTHETIC RESIN SUSPENDED IN A NON-VOLATILE PLASTICISERFOR THE RESIN, SAID RESIN BEING SUBSTANTIALLY INSOLUBLE IN THEPLASTICIZER AT ATMOSPHERIC TEMPERATURE BUT BEING COMPLETELY SOLUBLE INTHE PLASTICIZER AT AN ELEVATED FLUXING TEMPERATURE AND FORMING AT THISELEVATED TEMPERATURE A PERMANENT GEL WHICH BECOMES ELASTIC AND RUBBERYUPON SUBSEQUENT COOLING WHICH COMPRISES ARRANGING THE LINED CLOSURES ONAN OPEN MESH SUPPORT, SAID SUPPORT BEING OF SUCH OPEN MESH THAT WHEN ITIS LOADED WITH CLOSURES TO BE TREATED 30 TO 70% OF ITS AREA IS STILLFREE FOR THE PASSAGE OF AIR THERETHROUGH, DIRECTING A CONTINUOUS STREAMOF HEATED AIR UPON SAID CLOSURES AND AROUND AND PAST THE SAME, SAIDSTREAM CONTINUOUSLY DISCHARGING THROUGH SAID MESH SUPPORT, SAID AIRBEING HEATED TO A TEMPERATURE NOT SUBSTANTIALLY LESS THAN 300* F.SUFFICIENT TO FLUX THE LINING AND NOT GREATER THAN THE TEMPERATURE ATWHICH THE COATING ON THE CLOSURES WOULD DISCOLOR WITHIN A HEATING TIMEOF TWO MINUTES, SAID FLOW OF AIR HAVING A VELOCITY THROUGH THE FREEAREAS OF THE SUPPORT IN EXCESS OF 1500 FEET PER MINUTE AND SUFFICIENT TOCAUSE THE CLOSURES TO ATTAIN A TEMPERATURE WITHIN 5* F. OF THETEMPERATURE OF THE HEATED AIR WITHIN A PERIOD NOT EXCEEDING 60 SECONDS,REMOVING THE FLUXED CLOSURES FROM THE STREAM OF HEATED AIR WITHIN APERIOD SUCH THAT THE OVERALL TIME OF EXPOSURE TO THE HEATED AIR IS LESSTHAN TWO MINUTES AND COOLING THE CLOSURES.